A photographic light-sensitive material comprising a support and a photographic layer is liable to have a static charge accumulated thereon by contact friction with or peeling from a similar or different material during manufacture and use. This accumulated static charge causes many troubles. The most serious trouble is that a static charge accumulated before processing is discharged to sensitize a light-sensitive layer and form dot-like spot or dendritic and plumose line speckles when subjecting a photographic film to development processing.
This is a so-called static mark, and it markedly damages the commercial value of a photographic film. In some cases, the commercial value is completely lost. This phenomenon does not become clear until development is carried out and accordingly is a very troublesome problem. Further, this accumulated static charge causes secondary problems such as dust sticking on a film surface and difficulty in obtaining uniform coating.
As described above, such static charge is often accumulated during the manufacture and use of a photographic light-sensitive material. It is generated by, for example, the frictional contact of a photographic film with a roller and the peeling of an emulsion layer from a support during the steps of winding and rewinding of a photographic film. Further, the static charge is generated due to peeling of an X-ray film by contact with a machine part in an automatic camera or a fluorescent sensitive paper. In addition, it is generated by contact with a packaging material.
Static marking of a photographic material, which is caused by an accumulated static charge, is increased by the increase in the sensitivity and processing speed of a photographic light-sensitive material. Especially in recent years, the inclination toward high sensitivity for a photographic light-sensitive material and the increased chances to have the severe handling such as high speed coating, high speed photographing and high speed automatic development processing further accelerates the generation of static marking.
In order to remove the problems caused by a static charge, an antistatic agent is preferably added to a photographic light-sensitive material. However, the antistatic agents generally used in other fields cannot necessarily be applied as antistatic agents for a photographic light-sensitive material, since they must satisfy various requirements which are specific to a photographic light-sensitive material. That is, an antistatic agent which can be applied to a photographic light-sensitive material must have, for example, no bad influence on photographic properties such as the sensitivity of a photographic light-sensitive material, fog, graininess and sharpness, no bad influence on the layer strength of a photographic light-sensitive material (that is, no liability that a light-sensitive material is scratched by rubbing and scratching), no bad influence on anti-adhesiveness (that is, no liability that the surfaces themselves of the photographic light-sensitive materials or the surface thereof and that of another material are adhered), no acceleration of the deterioration of a processing solution used for a photographic light-sensitive material, and no deterioration of the adhesion strength between the respective component layers. Thus, the application of the antistatic agent is subjected to many limitations.
One method for eliminating the problems caused by a static charge is to increase the electroconductivity of the surface of a photographic light-sensitive material to discharge the static charge after only a short period of time (i.e., before an accumulated static charge is discharged). Accordingly, methods for increasing the electroconductivity of a support and various coated surface layers have previously been considered, and one method which has been tried is to utilize an ionic polymer.
The attempts to apply an anionic polymer having a carboxyl group for preventing a static charge in a photographic light-sensitive material are disclosed, for example, in JP-B-57-53587 (the term "JP-B" as used herein means an examined Japanese patent publication), and JP-B-57-15375, German Patent 1,745,061, JP-B-49-23827, JP-B-55-14415, and JP-B-55-15267, JP-A-48-89979 (the term "JP-A" as used herein means an unexamined published Japanese Patent Application), U.S. Pat. Nos. 2,279,410 and 3,791,831, and JP-B-47-28937.
However, these polymers are water soluble, and problems arise when a silver halide photographic light-sensitive material in which these polymers are present in an amount sufficient for obtaining a necessary antistatic property is subjected to development processing, whereby these polymers are eluted in an aqueous development processing solution and are accumulated therein to stain a silver halide photographic light-sensitive material which is subsequently subjected to development processing, and a small -elution spot remains on the silver halide photographic light-sensitive material from which the polymers were eluted to generate a cloud thereon.
Further, there has been the problem that these polymers are diffused from the layer of a silver halide photographic light-sensitive material to which these polymers are added to the other layers, so that the antistatic property is markedly lowered.
In order to solve these problems, attempts to convert these polymers to crosslinked latexes by using an ethylenically unsaturated monomer have so far been made to some extent. For example, it is disclosed in U.S. Pat. No. 4,301,240 that the conversion thereof to a crosslinked polymer is possible with the following methods (a) and (b), and it has been possible to solve the above various problems concerning the water soluble anionic polymers:
(a) the method in which acrylic acid or methacrylic acid is subjected to a reverse phase emulsion polymerization in a water-in-oil emulsion together with a crosslinking monomer in the presence of an alkali and a surface active agent to prepare a dispersion of a crosslinked polymer, and then the dispersion is broken to redisperse these polymer particles in water; and
(b) the method in which a short chain aliphatic ester of acrylic acid or methacrylic acid is subjected to an emulsion polymerization in an oil-in-water emulsion (regular phase) together with a crosslinking monomer in the presence of a surface active agent, and then an alkali is added to saponify the short chain aliphatic ester portion of acrylic acid or methacrylic acid.
However, all of the above methods have the problems that the production thereof is troublesome and, in addition, that they require very expensive manufacturing costs. That is, in the method (a), a large amount of an organic solvent is needed in carrying out the reverse phase polymerization, and further the operation to break the dispersion and redisperse the polymer particles in water is necessary.
Meanwhile, in the method (b), stirring for a long time under heating at a high temperature has to be continued for saponifying a short chain aliphatic ester of acrylic acid or methacrylic acid. According to the examples of U.S. Pat. No. 4,301,240, a long time of 45 hours at a high temperature of 125.degree. C. is needed.
Thus, the operations are troublesome in any of the above methods, and in addition, the production costs are very expensive. The increase in the production cost of a crosslinked polymer results naturally in the increase in the production cost of a photographic light-sensitive material in which the crosslinked polymer is used, and the commercial value thereof is damaged so much. Accordingly, it is strongly desired to manufacture the crosslinked polymer at an inexpensive cost.
The countermeasure against this problem is disclosed in JP-A-61-296352, in which a monomer having a carboxyl group (for example, acrylic acid and methacrylic acid) is subjected directly to an emulsion polymerization in an oil-in-water emulsion (regular phase), and then, an alkali is added to prepare a crosslinked polymer dispersion. This methods can provide a polymer having an inexpensive production cost, no problem of layer peeling, and an excellent antistatic property.
It has been found, however, that where the above material is used as an antistatic agent (particularly for a side opposite to a silver halide emulsion layer), film curling after processing becomes large, and that in case of a roller transportation type automatic developing machine, film becomes folded in some cases. A large amount of a hydrophobic crosslinking monomer is needed for preparing a crosslinked latex in a regular phase emulsion polymerization from acrylic acid and methacrylic acid, which are water soluble monomers. Accordingly, the latex particles thus prepared are highly crosslinked.
It is considered that where such an anionic latex dispersion is applied to a back layer as an antistatic agent, development processing causes curling (a curvature of the film which is generated due to the difference between the extensions of the inside and outside thereof) because of a notably small swelling rate of the back layer side against that of the silver halide emulsion layer side. A photographic light-sensitive material is needed to have no curling which is generated due to variations of temperature and humidity not only after processing but also during storage, and therefore if countermeasures such as increasing the amount of gelatin in the back layer and raising the hardening degree of the emulsion layer side are taken to prevent curling after processing, curling during storage is another problem.
Also, the reduction of a hydrophobic crosslinking monomer has the problem that while it can provide an effect for increasing the swelling rate of the layer containing an antistatic agent and preventing curling to some extent, the amount of an acid component which is converted to a crosslinked particle is reduced, and the ratio of a water soluble monomer is resultantly increased, and therefore the above problem attributable to the water soluble monomer results.